Modern chemical and petroleum refineries continually seek to recover and use waste heat energy from various operations in order to improve plant efficiencies and to lower costs. Unfortunately, temperature limitations of various process units in the plants preclude the use of waste heat generated by incinerators and other high temperature sources. For example, alkanolamine solutions, commonly used to remove acid gases from raw natural gas, begin to degrade when exposed to temperatures in excess of 325° F. Accordingly, the regeneration process must be closely monitored to ensure that temperature of the applied heat energy remains in the range of about 275° F. to about 350° F. As known to those skilled in the art, the temperature of the applied heat energy may range slightly above the degradation temperature of the alkanolamine solution in order to accommodate heat lost to the walls of the regeneration unit.
In a typical regeneration process, a “rich amine” (an alkanolamine solution containing large quantities of acid gases) is converted to a “lean amine” (an alkanolamine solution stripped of acid gases) in an amine still, also referred to as a stripper column. The amine still typically operates at a temperature of about 250° F. and a pressure of about 20 to 30 psig. Heat energy is applied to the amine still by directing the amine solution through a heat exchanger known as an amine reboiler. In view of the operational limits of the alkanolamine regeneration process, recovered waste heat from incinerators and other similar units is not currently used to heat the amine reboiler.
Thus, readily available sources of high temperature waste heat in acid gas treatment facilities such as, but not limited to, the sulfur incinerator, the BTEX incinerator and engine exhaust systems are not integrated with the alkanolamine regeneration process. The BTEX incineration converts natural gas contaminants such as benzene and alkylbenzenes to CO2 and H2O. Both the sulfur and BTEX incineration processes operate in excess of 1200° F. producing a high temperature vent gas. However, as noted above, use of the high temperature vent gas in the alkanolamine regeneration process is not currently practiced due to the temperature limitations imposed by the temperature sensitivity of the alkanolamine solution.
Steam is one preferred fluid for transporting heat energy to an amine reboiler or other similar heat exchange units. However, steam plants are not present in all refineries and chemical plants. In view of the expense to construct, operate and maintain a traditional steam plant, many operators prefer to use other heat sources for temperature sensitive solutions such as alkanolamines. However, such heat sources must provide even heating of the regeneration system or localized overheating will lead to degradation of the temperature sensitive solution solution.
Thus, there is a need for a method and system for recovering waste heat from a high temperature source, such as the BTEX incinerator, and using the recovered heat in a process that does not tolerate high temperatures, such as an alkanolamine regeneration process. The method and system must provide for the even application of heat energy to the regeneration system in order to preclude degradation of the solution being regenerated. Additionally, it would be desirable for the system to be suitable for retrofitting to currently existing processing units.